Childhood obesity rates continue to increase in the U.S. and internationally, particularly among youth in middle childhood and adolescence, with alarming anticipated health consequences. Such increasing prevalence of obesity requires a systematic evaluation of the factors contributing to this epidemic, particularly environmental factors that are amenable to policy change. Recent empirical evidence, paired with emerging concepts that integrate urban planning and public health, suggests that adult obesity and weight-related behaviors are related to neighborhood built environment characteristics. Very few studies have evaluated the association between built environmental and child weight status or change in child weight status. The present study aims to 1) evaluate the association of neighborhood-level physical activity and nutrition environment with children's weight status after controlling for known individual and familial risk factors, and 2) evaluate the ability of neighborhood-level environmental factors to predict the change in children's weight status over a 2-year period. This will be a multi-level observational study. Census block groups in two distinct regions in the U.S. (Cincinnati, OH & San Diego, CA) will be screened, clustered to form neighborhoods, and selected for study based on the built environment constructs of walkability (combination of street connectivity, residential density, land use mix, and retail floor area ratio), public recreation space quality, and nutrition environment quality. Walkability indices will be created through existing parcel-level and street network information in these regions. Public recreation space and nutrition environment quality indices will be created using established psychometrically sound direct observation instruments. Forty neighborhoods (n=20 per region) with socioeconomic diversity will be selected for study based on these built environment constructs, with additional environmental variables also collected (e.g., crime). Twenty children 6-10 years old and a parent will be randomly selected from each of the study neighborhoods (n=800 total pairs). Child weight status, physical activity, and dietary intake will be directly assessed at baseline and 2 years following baseline. Home and school environment factors related to their child's weight status will be reported by parents, and parental weight status, early child feeding experiences, and demographics will be obtained. The proposed trans-disciplinary project team combines expertise in studying obesity, physical activity, nutrition, and their relation to built environment factors. The proposed study addresses critical unanswered questions regarding associations of neighborhood built environment with childhood obesity and related behaviors. The proposed detailed evaluations of multiple dimensions of the built environment and use of best-available measures will advance science and provide information that can be used by policymakers to contribute to controlling the epidemic of childhood obesity.